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William Sager, a professor of geophysics in the UH Department of Earth and Atmospheric Sciences, has spent the last 35 years going to sea and exploring the oceans using geophysical techniques. When it comes to looking at the ocean bottom in the southeastern Indian Ocean, where searchers are looking for missing Malaysian Airlines Flight 370, Sager can say “been there, done that.”

﻿In 2007, Sager was chief scientist of a cruise on the research vessel Roger Revelle during a 50-day cruise that passed through part of the search area. Owned by the U.S. Navy’s Office of Naval Research, this ship’s mission was to collect sonar and seismic imaging data showing the seafloor, sediment layers and faults caused by plate tectonics.

“One thing that stood out about the cruise was that it was one of the roughest I have been on,” Sager said. “It wasn’t dangerous, but there were large waves for much of the time, and you just get tired of constantly holding on and being thrown into bulkheads.”

Although he has not searched for airplanes, he uses sound waves, or sonar, to image the bottom of the ocean and has worked with systems like those being deployed today. Sager commiserates with searchers looking for the proverbial needle in the haystack and says, “Imaging the ocean bottom is incredibly difficult, time consuming and expensive. Without a break to give them a clue about where to look, I doubt the wreckage will be found. The recent pinger signals are that break. If they get a clue on the location from the pingers, they have a chance, but it still may take a long time and a lot of effort.”

Sager says the fundamental problem with searches beneath the sea is that the water gets in the way. It does not allow light to penetrate far, so sonar must be used for imaging. Even with sonar, however, none exists that can image small objects on the bottom of the deep ocean from the surface. High-frequency sonars, he says, are the best for imaging, but high-frequency sound quickly dies out, so the sonar has to be close to the seafloor, which is technically challenging. Either the sonar has to be tethered to the ship by a long cable, restricting the speed and maneuverability of the ship, or a robot submarine, known as an autonomous underwater vehicle (AUV), must be sent to the bottom. Even the instrument, itself, is slow, going about the speed of a slow jog.

“With an AUV it is possible to cover an area of about 60 square kilometers, which is 23 square miles or about the size of Manhattan Island. Although this sounds like a lot, a search area that’s about 500 miles on a side contains almost 11,000 Manhattans, so a big search is daunting,” Sager said. “Putting it further into perspective, there are probably only a few dozen deep water AUVs available out there, and each one needs a ship and crew, so you’re looking at many thousands of man hours and millions of dollars to conduct that kind of search.”